The present invention relates generally to using inert fillers dispersed throughout a polymeric resin and more particularly relates to using a waste material, coal fly ash, as such filler.
Chemical agents, such as organo-functional silanes, stearic acids and organotitanates have been applied to a number of powdered inorganic materials; namely glass, sand, metals, clays and metallic oxides. These chemically pretreated surfaces promote an enhanced bond between the inorganic filler particles and the organic polymer or resin. At present, chemical surface pretreatment of coal fly ash has not been reported or commercially used and there are contraindications to the use of coal fly ash as a filler for polymers and resins.
Known related art includes U.S. Pat. Nos. 3,846,366 and 3,991,005 issued respectively on Nov. 5, 1974 and Nov. 9, 1976 to Richard A. Wallace, together with articles entitled: A NEW COUPLING AGENT FOR EXTENDERS, FILLERS, AND REINFORCEMENTS USED IN POLYMERS, J. Elastomers and Plastics, Vol 8, 30 Jan. 1967 by S. J. Monte, G. Sugerman and P. F. Bruins: and, SILANE ADHESION PROMOTERS, Modern Plastics Encyclopedia, 260, 1974-75 by C. A. Bergeson.
Coal fly ash is produced as waste residue during operation of coal-fired power houses. It is collected by mechanical collectors, bag filters or electrostatic precipitators suitably mounted in flues of the boilers of such installations.
About six to ten percent of the coal fed to the boilers must ultimately be disposed of as coal fly ash. A typical installation will regularly produce many tons of fly ash per day. The power houses must absorb the costs of labor and equipment for disposal of this ash. Further, ecological considerations are compounding the problem by making it more difficult to locate acceptable disposal sites.
Several alternatives have been suggested. Public utilities have used coal fly ash as both concrete additives and as components in highway paving compounds. More importantly there have been questions of using coal fly ash to fill polypropylene. See FLY ASH FILLED POLYPROPYLENE, General Motors Research Publication GMR-2578, Oct. 27, 1977 by R. L. Kaas.
Several contraindications are present which have heretofore taught against the use of coal fly ash as an elastomer or polymer filler. Primarily, coal fly ash has inherent variability in its typical chemical composition, especially the carbon content. Table 1 lists typical chemical components of coal fly ash.
TABLE 1 ______________________________________ Silica 47.4%; Alumina 22.7%; Ferric Oxide 16.7% Sulfer Trioxide 1.2%; Magnesium Oxide 0.1%; Calcium Oxide 1.0%; Titanium Oxide 1.9%; Metals and other Oxides 2.0%; Moisture 1.3% and Unburnt Carbon 5.7% ______________________________________
Chemical variability causes jaggedness which causes abrasiveness (for example unburnt carbon) of coal fly ash could yield changes in rheological flow as well as variable mechanical properties of any resultant polymeric composite. Specifically, as noted by R. L. Kaas, unnotched impact and wet strengths of coal fly ash-filled thermoplastics (assuming identical percentage loading and particle size and distribution) are markedly lower than those for talc-filled thermoplastics.
Poor compatibility of uncoated fly ash with an organic phase necessitates a pre-mixing step or two-roll mill at elevated temperature (R. L. Kaas, General Motors Research Publication).
Flexual strengths and elongations at break are also inferior to those of talc-filled thermoplastics as is also noted by R. L. Kass. These inferior mechanical properties are due to inefficient wetability and poor to moderate bonding between two dissimilar surfaces (those of the coal fly ash and of the organic polymer. It is noted that water has mechanical destructive influence in the already poor adhesion between polymer and coal fly ash.
Still another contraindication is the high abrasion resistance of the rough and irregular coal fly ash which typically has predominately irregular, jagged particles with length to width ratios of about one. This property, in machine-assisted polymer processing, could cause extreme wear of molding machines thereby causing frequent replacement of worn parts. For each of these reasons, and because known coating methods are cost prohibitive, polymer processors and compounders do not use the non-uniform and variable coal fly ash. Conversly, increasing relative scarcity of petroleum together with ecological and disposal costs considerations indicate that if the contraindications could be overcome, the resultant coal fly ash-filled polymers and elastomers would be of significant importance.